Magnetic Metal Complexes

　Magnetism is mainly classified into five categories: paramagnetism in which unpaired electrons are randomly oriented, ferromagnetism in which unpaired electrons are oriented in the same direction, antiferromagnetism in which unpaired electrons are oriented in antiparallel direction, ferrimagnetism in which unpaired electrons with different magnetic moments are oriented in antiparallel direction, and diamagnetism without unpaired electrons. An application of ferromagnet for electronics is a magnetic disk that is further developed to enhance memory capacity. Many Prussian blue analogues formulated as M₄[M(CN)₆]₃ are ferromagnets and ferrimagnets.^1,2)
　Although neodymium magnets and ferrite magnets are magnetic materials based on inorganic solids, magnetic materials using molecular metal complexes have been also developed. Since a molecular magnetic material has a molecular unit, one advantage is that a chemical modification of the unit molecule controls physical properties. Furthermore, a molecular material can fabricate a device at low cost. Miller et al. observed a ferromagnet of the charge transfer complex derived from metallocene and tetracyanoethylene (TCNE) or tetracyanoquinodimethane (TCNQ).^3,4) Single molecule magnets (SMM) in which a single molecule behaves as a magnet, were intensively investigated from 1993.^5,6) The SMM is a specified material obtained from a molecular compound, and the application may be high-density information media. Single-chain magnets (SCM) are obtained from a one-dimensional assembly of magnetic complexes.⁷⁾ Kato et al. reported that physical properties of the metal complex salt of the 1,2-dithiolene ligand formulated as (Cation)[Pd(dmit)₂]₂ in which the anion radical of the dimer [Pd(dmit)₂]₂ shows paramagnetism, antiferromagnetism, superconductivity and spin liquid state.⁸⁾